Permanent magnets based on compositions containing iron, neodymium and/or praseodymium, and boron are known and in commercial usage. Such permanent magnets contain as an essential magnetic phase grains of tetragonal crystals in which the proportions of, for example, iron, neodymium and boron are exemplified by the empirical formula Nd.sub.2 Fe.sub.14 B. These magnet compositions and methods for making them are described by Croat in U.S. Pat. No. 4,802,931 issued Feb. 7, 1989. The grains of the magnetic phase are surrounded by a second phase that is typically rare earth-rich, as an example neodymium-rich, as compared with the essential magnetic phase. It is known that magnets based on such compositions may be prepared by rapidly solidifying, such as by melt spinning, a melt of the composition to produce fine grained, magnetically isotropic platelets of ribbon-like fragments. Magnets may be formed from these isotropic particles by practices which are known, such as bonding the particles together with a suitable resin.
Although the magnets formed from these isotropic ribbons are satisfactory for some applications, they typically exhibit an energy product (BHmax) of about 8 to about 10 megaGaussOersteds (MGOe), which is insufficient for many other applications. To improve the energy product, it is known to hot press the isotropic particles to form magnets having an energy product of about 13 to about 14 MGOe and magnetic remanences on the order of about 8 kG.
However, there are applications when it would be desirable that such hot pressed magnets have higher magnetic remanence values. As an example, if the hot pressed magnet is used in an application at or near its maximum magnetic remanence, it may be desirable to increase its magnetic remanence so as to increase the capability of the magnet.
Conventionally, for hot pressed magnets of the iron-rare earth metal type, the total rare earth constituent is greater than about 25 percent, most typically greater than about 29 percent, by weight. This is true since compositions containing lower amounts of the rare earth constituents contain lesser amounts of the intergranular phase, and therefore require higher pressing temperatures, which are detrimental to the life of the hot pressing punches and add undesirable costs to the pressing process. Thus, the prior art has generally always taught that hot pressed permanent magnet compositions of this type must contain, as a minimum, at least 25 percent rare earth constituent.
Yet, it would be desirable to provide a means for increasing the magnetic remanence of a hot pressed magnet, such as to a value of at least about 9 kG or 10 kG, while simultaneously reducing or minimizing the amount of rare earth within the compositions, since the rare earth constituents are typically much more costly as compared to the other constituents. However, the means for accomplishing such an increase in magnetic remanence should not result in increased hot pressing temperatures.